From the fact that stress can cause fatigue and depression, great importance is placed on stress check in recent years. However, there is a problem in that it is difficult to check whether a person is under stress by other persons owing to the fact that the person himself/herself may not be aware of the stress or that the stress is a subjective matter, for example. Under these circumstances, there is a demand for the establishment of a method for checking stress objectively.
It is known that, when humans feel stress, secretion of α-amylase in saliva increases. On this account, there has been an attempt to evaluate stress indirectly by measuring α-amylase in the saliva. Specifically, an ELISA method using an antibody against α-amylase as an antigen has been reported (Non-Patent Document 1).
However, antibodies are proteins and thus have a problem in stability. Accordingly, it is difficult to use an antibody in a test method that can be carried out easily at low cost.